Changes in Cytosolic pH within Arabidopsis Root Columella Cells Play a Key Role in the Early Signaling Pathway for Root Gravitropism

• Published in: Plant physiology (Bethesda) 1999-12, Vol.121 (4), p.1291-1298
• Main Authors: Amie Caroline Scott, Allen, Nina Strömgren
• Format: Article
• Language: English
• Subjects: Acidification; Arabidopsis - cytology; Arabidopsis - growth & development; Arabidopsis - physiology; Biological and medical sciences; Cell Biology and Signal Transduction; Curvature; Cytosol - physiology; Fundamental and applied biological sciences. Psychology; Gravitropism; Gravitropism - physiology; Gravity perception; Hydrogen-Ion Concentration; Kinetics; Life Sciences (General); Microscopy, Fluorescence; Movements; Plant cells; Plant physiology and development; Plant roots; Plant Roots - cytology; Plant Roots - growth & development; Plant Roots - physiology; Plants; Root cap; Root growth; Signal Transduction; Space life sciences; Time Factors
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.121.4.1291

Ratiometric wide-field fluorescence microscopy with 1′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran demonstrated that gravistimulation leads to rapid changes in cytoplasmic pH (pHc) in columella cells of Arabidopsis roots. The pHc of unstimulated columella cells in tiers 2 and 3, known sites of graviperception (E. B. Blancaflor, J. B. Fasano, S. Gilroy [1998] Plant Physiol 116: 213-222), was 7.22 ± 0.02 pH units. Following gravistimulation, the magnitude and direction of pHc changes in these cells depended on their location in the columella. Cells in the lower side of tier 2 became more alkaline by 0.4 unit within 55 s of gravistimulation, whereas alkalinization of the cells on the upper side was slower (100 s). In contrast, all cells in tier 3 acidified by 0.4 pH unit within 480 s after gravistimulation. Disrupting these pHc changes in the columella cells using pHc modifiers at concentrations that do not affect root growth altered the gravitropic response. Acidifying agents, including bafilomycin A1, enhanced curvature, whereas alkalinizing agents disrupted gravitropic bending. These results imply that pHc changes in the gravisensing cells and the resultant pH gradients across the root cap are important at an early stage in the signal cascade leading to the gravitropic response.